This invention relates to an apparatus and a process for cleaning of air by removing solvents from the air.
In many industries there is a need for air cleaning equipment. An automobile manufacturing plant, for example, includes spray painting facilities, and there is a sizable amount of paint solvent contained in the air leaving the paint spray booths. EPA regulations require that the organic solvent be removed from the air before it is discharged into the atmosphere. In this situation, a high volume of air having a relatively low concentration of solvent must be processed.
Prior art systems have been provided for removing an organic solvent from an air stream, but, in general, such systems have been designed for the purpose of recovering solvent from air having a high concentration of solvent. Such systems have included, for example, a bed of carbon and ducts for feeding the air stream through the bed. The carbon adsorbs the solvent but passes the air, and when the carbon is saturated, the solvent is stripped or desorbed from the carbon. A common method of stripping the solvent is by steam heating the carbon, the heat serving to vaporize the solvent and thereby permit its removal. The carbon is then reused, and the solvent vapor is cooled to permit collection of liquid solvent. A system of this nature may include two carbon beds, one bed being stripped while the other adsorbs solvent.
Another system that has been used is one wherein an inert gas is heated and the hot gas is forced through a solvent-laden carbon. The gas both vaporizes the solvent and sweeps the vapor out of the carbon bed.
Prior art systems of the above character have been designed to handle relatively small volumes of air having relatively high concentrations of solvents. Such systems have also required relatively expensive and complex components, and they have been relatively inefficient because they operate by heating one medium and then using the heated medium to heat the carbon. Prior art systems also have the disadvantage that they have a relatively slow response to changes in the operating conditions, and their start-up time is relatively long.
It is a general object of this invention to provide an improved system for efficient processing of a high volume of air having a very low concentration of solvents.